Automotive-type alternators, particularly three-phase alternators, frequently include diode rectifier units directly secured to the structure; they may, also, have voltage regulators of the semiconductor type secured thereto. The voltage regulator is usually secured to the outside of the housing shell, for example to one of the end bells of the alternator. The voltage regulator is thereby cooled, by such cooling air as passes by or through the alternator itself. The cooling air enters the alternator through openings, typically in slit form, formed in the end bells of the structure. The cooling air thus passes the voltage regulator and is then, inwardly of the end bell, directed to cool the bearings, the rotor, and the slip rings and brush region of the structure.
Alternators are frequently installed in environments where the circulating air itself is already hot. This may interfere with cooling of the alternator and, in order to supply air to the alternator at ambient temperature, it has been proposed to attach an air supply duct to the alternator end bell, located axially behind the alternator itself to supply cooling air thereto from a region of the vehicle, with which the unit is used, where the general air temperature is at ambient level, rather than already heated. Such arrangements are difficult to assemble and install in automotive vehicles, and require an excessive amount of space for their attachment to the alternator structure itself. If the alternator is combined with a voltage regulator, it may be hidden within the air supply structure and thus difficult to maintain or replace, and additionally may be subjected to air flow which is contaminated, thus causing, potentially, damage to the voltage regulator.